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Abstract:

Improved high speed helium leak-detection system for storage tanks
comprising a mobile enclosure for operation of electrical components of
leak detection sensors in Class 1, Division 1, Group D hazardous
locations, comprising a rapid exchange purge assembly having pressure
control valves, pressure reference controller and vent, a mechanically
actuated vortex-type cooler, a helium leak detector having a pumping
manifold connected to a sniffer probe hose to provide sample gas from the
tank probe to a pair of pumps oriented in parallel. The first pump,
downstream of the helium leak detector, draws a sample through the
detector, and a second pump provides a rapid transfer of probe sample.
The enclosure includes a controller, display and alarm. The enclosure is
maintained overpressure to prevent infiltration of hazardous vapors and
is continuously purged with com-pressed air. The system provides response
time of about 2 seconds, a 5-fold improvement over current systems.

Claims:

1. A high speed leak detection system for hazardous environment location
detection of He tracer gas leaks in vessels, comprising in operative
combination: a. a mobile Class 1 Hazardous Location Enclosure in which
all vias are sealed and all access panels and widows have seals to
provide in operation a sealed mobile enclosure; b. a He tracer gas probe
and having a negative pressure nozzle for sniffing He leaking from He
tracer gas-pressurized vessels to provide probe samples; c. a conduit
having a first end connected to an output of said probe unit for
conveying said probe samples from sniffed vessels and having a second,
distal conduit end connectable to an input manifold disposed in said
sealed mobile enclosure; d. a pumping manifold system disposed in said
enclosure having an inlet connected to said second, distal end of said
conduit to receive said probe samples; e. a detector unit disposed in
said enclosure including a He sensor which produces a He detection signal
and converts said signal into quantitative leak rates; f. said manifold
system including a pair of pumps oriented in parallel, in which a first
pump is disposed downstream of said detector unit to draw a portion of
said probe sample into contact with said He sensor, and a second pump
providing a negative pressure rapid transfer boost of said probe sample
from said probe unit nozzle to said manifold to reduce the transit time
from the probe to the He sensor to permit near real time He leak
detection; and g. said enclosure including an inlet for introduction into
said enclosure interior of compressed filtered dry air, or inert gases
which exclude He, to provide an internal overpressure in said enclosure
to prevent infiltration of hazardous vapors from the location where the
enclosure is operating and to permit operation of electrical components
for operation of said pumps and He sensor system.

2. A high speed leak detection system For hazardous environment location
detection of He tracer gas leaks as in claim 1 wherein said enclosure
includes means for maintaining said internal overpressure relative to the
ambient environment in which said enclosure is located at a preselected
value.

3. A high speed leak detection system for hazardous environment location
detection of He tracer gas leaks as in claim 2 wherein said internal
overpressure means includes an inlet pressure control valve and a
mechanical enclosure valve to vent overpressure above a preselected
value.

4. A high speed leak detection system for hazardous environment location
detection of He tracer gas leaks as in claim 3 which includes a system
for initiation and control of a cycle of rapid exchange of said inlet
compressed air or inert gas to purge said enclosure interior with
multiple volumes of said compressed air or gas.

5. A high speed leak detection system for hazardous environment location
detection of He tracer gas leaks as in claim 4 which includes a
mechanically actuated vortex cooler employing said inlet compressed air
or inert gas to maintain the internal temperature of said enclosure
within a predetermined range.

6. A high speed leak detection system for hazardous environment location
detection of He tracer gas leaks as in claim 5 which includes a switch
connected to a facility mains power input to said enclosure interior for
operation of said leak detection system, said switch is responsive to
preselected enclosure internal pressure values in order to cut off power
at initiation of said rapid exchange cycle and to automatically restore
power when preselected conditions are re-established internal to said
enclosure

7. A high speed leak detection system for hazardous environment location
detection of He tracer gas leaks as in claim 4 wherein said rapid
exchange system includes ambient atmosphere and enclosure internal
pressure reference sensors.

8. A high speed He leak detection system as in claim 6 wherein said
enclosure includes a controller, said controller also including a
display, control parameter input means and an alarm, said controller
linked electrically to said pump manifold system, said internal
overpressure means, said rapid exchange purge system and said He leak
detection system, said controller being selectively configurable for
operation of said leak detection system, including presetting a leak rate
detection level for triggering an alarm.

9. A high speed He leak detection system comprising: a sealed, mobile,
purged air enclosure permitting operation of electrical components
thereof in Class 1, Division 1, Group D Hazardous Locations; said
enclosure including a pair of vacuum pumps disposed in parallel drawing a
sample stream of gases from a He sniffer probe assembly; a first pump
located downstream of a He leak detector in said enclosure that is
configured to draw a minor portion of said sample stream through said He
detector; and a second pump configured to draw a major portion of said
sample stream and exhaust said major portion without sampling directly to
the exterior of said enclosure; said dual pump induction of sample stream
from said sniffer permitting high speed response of said detector on the
order of about 2 seconds for probe sample stream hose line lengths on the
order of 60'; and a controller disposed in said enclosure for
configuration of operation of said leak detection system including
presetting a leak rate level for triggering an alarm at said sniffer
probe assembly.

10. A high speed He leak detection system as in claim 9 wherein said
sealed mobile enclosure includes a rapid exchange purge system configured
to maintain the pressure in said enclosure at a predetermined pressure
greater than atmospheric to prevent infiltration of hazardous vapors into
said enclosure to permit electrical components of said system to operate
in said hazardous locations, a vortex cooler configured to automatically
maintain the temperature inside said enclosure at a predetermined
temperature, and said controller is configurable to preset enclosure
pressure.

11. A method of high speed detection in hazardous environments of He
leaks from vessels pressurized with He tracer gas, comprising the steps
of: a. pressurizing a vessel to be tested for leaks with a He-containing
tracer gas; b. sampling selected areas of the exterior of said vessel to
be tested with a negative pressure probe to obtain a sample stream volume
of gas that may contain He leaking from said test vessel; c. transferring
to a purged air, sealed mobile enclosure said entire volume of said
sample stream; said mobile enclosure having disposed therein a manifold
connected to a first negative pressure device; d. splitting-off at said
manifold a minor portion of said entire sample stream as a detection
stream; e. drawing said detection stream through a He sensor by a second
negative pressure device, said He sensor providing a signal upon
detection of the presence of trace gas He in said detection stream, and
said He sensor and said second negative pressure device being disposed
within said mobile enclosure; f. converting in near real time said
detection signal into quantitative leak rates of said test vessel; and g.
introducing compressed filtered dry air or inert gas other than He into
said sealed enclosure to provide an internal overpressure therein to
prevent infiltration into said enclosure interior of hazardous vapors
from the location where the enclosure is located and permit the use of of
electrical components required for said negative pressure and sensor
devices.

12. A method of high speed detection in hazardous environments of He
leaks as in claim 11 which includes maintaining said internal
overpressure at a selected value relative to the ambient environment in
which said enclosure is located to prevent said infiltration of hazardous
vapors into said enclosure interior.

13. A method of high speed detection in hazardous environments of He
leaks as in claim 12 which includes the step of rapid exchange of said
inlet compressed air or inert gas to maintain the internal temperature of
said enclosure within a predetermined range and to purge said enclosure
of hazardous vapors.

14. A method of high speed detection in hazardous environments of He
leaks as in claim 13 which includes the steps of monitoring the
temperature in said enclosure, and cooling the interior atmosphere of
said enclosure to maintain said internal temperature within a
predetermined range.

15. A method of high speed detection in hazardous environments of He
leaks as in claim 15 which includes the step of controlling said
enclosure internal atmosphere pressure so that where said internal
pressure falls below a preselected first, low pressure value, compressed
air or inert gas is inlet to the enclosure until the internal enclosure
pressure reaches a preselected second, trigger pressure value to initiate
a rapid exchange purge sequence to commence for a preselected time period
resulting in multiple enclosure gas volume exchanges, during which if the
internal enclosure press-are exceeds a preselected, third vent-trigger
value, an enclosure protection valve is opened to vent excess gases
pressure to the ambient atmosphere in which said enclosure is located,
and upon the end of said preselected purge sequence time period,
controlling the enclosure internal pressure to a preselected fourth
operating value.

16. A method of high speed detection in hazardous environments of He
leaks as in claim 15 wherein said step of controlling includes shutting
off power to said enclosure when the minimum acceptable pressure is
detected, maintaining power off during the rapid exchange sequence, and
restoring power at the end of said preselected purge sequence time
period.

17. A method of high speed detection in hazardous environments of He
leaks as in claim 16 wherein said low first pressure value is selected to
be about 0.15'' c.w., said second trigger pressure value is selected to
be about 2.5'' c.w., said third vent-trigger value is selected to be
greater than about 0.65'' c.w., and said fourth operating value is
selected to be on the order of about 1.5'' c.w.

18. A method of high speed detection in hazardous environments of He
leaks as in claim 14 wherein said internal enclosure temperature is
detected by a thermal sensor connected to an external vortex cabinet
cooler, actuating internal cooling by use of said compressed air or inert
gas provided to said enclosure.

19. A method of high speed detention in hazardous environments of He
leaks as in claim 13 wherein said rapid exchange is assisted by a
mechanical enclosure valve that vents overpressure from said enclosure
interior to the exterior.

20. A method of high speed detection in hazardous environments of He
leaks as in claim 11 which includes providing an audible and visual alarm
when a predetermined quantitative leak rate is detected.

Description:

CROSS REFERENCE TO RELATED APPLICATION

[0001] This is the Regular US Application corresponding to and claiming
priority from U.S. Provisional Application of the same title, Ser. No.
61/588,995, filed by the same inventor on Jan. 20, 2012, the disclosure
of which is incorporated by reference and the priority of which is
claimed under 35 USC §119 ff.

FIELD

[0002] The invention is related to the field of helium leak detection, and
more particularly to an improved, special purpose, high speed helium leak
detection system for detection of helium tracer leaks from helium/air
pressurized vessels, including fuel storage tanks that are located in
hazardous environments. The exterior of each vessel/tank is sniffed with
a negative pressure probe that draws in ambient air plus a sample of
trace helium leaking out of the tank. The probe sample is evaluated by
means of a helium-sensitive sensor which converts the sensor signal into
quantitative leak rates. The sniffer probe opening is at the outboard end
of a long line, and the response time to get the inlet sniffed gas to the
sensor is reduced to less than 2 seconds (<2 sec) by a secondary
pumping system. The pumps, electrical supply components and leak detector
are enclosed in a hazardous location enclosure that includes both a rapid
exchange purge system and an enclosure cooling system. The inventive
system includes a system display and a controller having configuration
and alarm functionality.

BACKGROUND

[0003] Storage vessels, and particularly aircraft fuel tanks, must be free
of leaks, even microscopic ones, to insure their integrity for operation
under harsh environments. In order to test the integrity of vessels/tanks
alter manufacture, or after use once put in service, leak detection
systems are used. Typically these have a long hose attached to a vacuum
pump to pull in a sample of gas and air. The hose terminates in a
defined-size metal tube terminating in a sniffer probe that functions as
an inlet nozzle. The vessel/tank to be tested is pressurized with a
selected mix of air and helium. Then the sniffer probe is guided over all
surfaces and outlet valves and lines of the tank to draw in samples of
gas, in the ease of a sound tank, having no leaks, ambient air, but in
the ease of a leaking tank, helium-laden air.

[0004] The probe sample is routed to a helium sensor which detects the
helium and can convert the detection signal into a quantitative rate of
leak. These helium sensors are relatively conventional, one type working
by ionizing a gas sample containing helium, passing the ionized sample
through a magnetic field and collecting the helium ions as they emerge to
produce an electric current which is used to drive an ammeter the values
of which are converted to quantitative leak rates. Another system rises a
membrane, which allows only Helium to pass through for detection.

[0005] A serious problem is presented by currently available helium leak
detections systems in that the hose line from the sensor to the probe tip
is required to be on the order of 10-50 feet in length to permit the
detection technician to climb up on aircraft wings to reach tanks that
are in service. A typical response time for a 10 foot snifter hose is
around 10 seconds, since it takes that long for a sniffed sample to be
delivered to the helium sensor. By that time the technician may have
moved on to a different area of the tank, so that an alarm means that the
technician must return to a previous area in order to pin-point the leak
location.

[0006] In addition, many tanks under test are located in hazardous
environments, such as Class 1, Division 1, Group D hazardous
environments, such as those involving volatile organic fuels or solvents.
Accordingly, the electrical equipment associated with the probe pump,
sensor, control system and alarm system cannot be used in such
environments. In order to service in such environments, present systems
require even longer hoses, or sequestration of the pump, sensor and
associated electrical systems in separate rooms.

[0007] Accordingly, there is a significant, unmet need to have a faster
response time in helium leak detection so that retracing a sampling path
is not required, and permits operating, portably, in hazardous
environments.

THE INVENTION

Summary, Including Objects and Advantages

[0008] The invention is directed to an improved, special purpose, high
speed helium leak detection system for detection of helium tracer gas
leaks trout storage vessels, such as fuel tanks, located in hazardous
environments. The inventive system comprises a special purged air
enclosure (also called a cabinet) that permits use of all electrical
components associated with leak detection sensors to be operated in Class
1, Division 1, Group D hazardous location environments. The enclosure is
mourned on wheels for mobility. The enclosure includes an enclosure
protection rapid exchange purge assembly with pressure control valves,
pressure reference controller and an enclosure protection vent, a cabinet
cooler, preferably a vortex-type cooler, that is thermally actuated
mechanically rather than electrically, a helium leak detection system
having a pumping manifold, the inlet of which is connected to the outlet
end of the sniffer probe hose. The pumping manifold provides the sample
gas from the vessel/tank probe to a pair of pumps oriented in parallel,
in which a first pump is disposed downstream of the helium leak detector
sensors to draw sample through the detector, and a second pump provides a
rapid transfer boost of the sample from the probe nozzle. The
enclosure/cabinet also includes an internally mounted controller having
an input keyboard for configuring the operation, a display, and an alarm.
The enclosure is maintained at a selected overpressure relative to the
ambient environment to prevent infiltration of hazardous vapors. The
enclosure overpressure is provided by facility compressed air, which is
typically dry, filtered fresh air. In the alternative, an inert gas, not
helium, may be used to provide the enclosure purge gas.

[0009] In operation, the storage vessels or tanks to be tested for leaks
are filled with an overpressure of a mixture of helium and air. The
exterior of each tank is sniffed with a negative pressure probe drat
draws in a sample of ambient air that would include traces of helium
leaking out of the tank. The probe sample is evaluated by means of a
helium-sensitive sensor which converts the sensor signal into
quantitative leak rates. The sniffer probe opening is at the outboard end
of a long hose line, approximately 60 feet in length. In the inventive
system, the response time to get the inlet sniffed gas to the sensor is
reduced to less than 2 seconds by the parallel secondary pumping system.
This is a 5 or more-fold reduction in response time, permitting near real
time sensing, as the residence of a probe in any one location on a tank
has a dwell time on the same order, e.g. 2-3 seconds.

[0010] In terms of operation of the inventive high speed He detection
method, the following steps occur:

[0011] 1. The minimum acceptable
pressure within the enclosure is 0.15'' c.w. If the pressure falls below
this value, then the power is shut down and the Rapid Exchange Sequence
is initiated. Air at 80 psig is switched on and introduced into the
cabinet.

[0012] 2. Once the internal enclosure pressure reaches 2.5''
c.w. the timer of the Rapid Exchange Sequence starts. The sequence lasts
for 15 minutes and results in approximately 4 cabinet volume exchanges.

[0013] 3. During the Rapid Exchange Sequence the pressure within the
enclosure can rise up to approximately 4.5'' c.w. The Enclosure
Protection Valve (EPV) is designed to open at 0.65'' c.w. in order to
protect the enclosure from overpressure and allow for the exchange of the
air volume. So, during most of the Rapid Exchange Sequence the EPV is
open and air from the enclosure is forced to escape, thus allowing for a
purging of the enclosure and the 4× volume change.

[0014] 4. After
the Rapid Exchange Sequence is completed (i.e. after 15 min) the pressure
inside the enclosure is allowed to drop down to 1.5'' c.w. This value is
set by the operator via the Enclosure Pressure Control Valve. The
electrical power is restored.

[0015] 5. In NORMAL operation the Purge
system will maintain the pressure within the enclosure at 1.5'' c.w. and
maintain the electrical power. If the enclosure pressure were to fall
below 0.15'' c.w. then the whole process would be repeated.

[0016] The wheeled hazardous location qualified enclosure of the invention
permits bringing the leak detection sensor system in close proximity to
the location of the vessels, which may be tanks on a large aircraft, or
in other hard-to-access locations.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The invention is described in more detail with reference to the
drawings, in which:

[0018] FIG. 1 is a schematic of the system architecture of the inventive
rapid response helium leak detection system as installed in a wheeled
Class 1, Division 1, Group D Hazardous Location Enclosure;

[0019] FIG. 2 is a block diagram of the operation of the inventive rapid
response helium leak detection system pressure and temperature control
system of FIG. 1;

[0020] FIG. 3 is a block diagram of the operation of the purge cycle of
the inventive enclosure purge system sub-assembly;

[0021]FIG. 4 is a block diagram of the operation of the vortex cooler
sub-system of the inventive enclosure; and

[0022]FIG. 5 is a block diagram of the operation of the leak detector
sub-system of the inventive enclosure.

DETAILED DESCRIPTION, INCLUDING THE BEST MODES OF CARRYING OUT THE
INVENTION

[0023] The following detailed description illustrates the invention by way
of example, not by way of limitation of the scope, equivalents or
principles of the invention. This description will clearly enable one
skilled in the art to make and use the invention, and describes several
embodiments, adaptations, variations, alternatives and uses of the
invention, including what is presently believed to be the best modes of
carrying out the invention.

[0024] In this regard, the invention is illustrated in the several
figures, and is of sufficient complexity that the many parts,
interrelationships, and sub-combinations thereof simply cannot be fully
illustrated in a single patent-type drawing. For clarity said
conciseness, several of the drawings show in schematic, or omit, parts
that are not essential in that drawing to a description of a particular
feature, aspect or principle of the invention being disclosed. Thus, the
best mode embodiment of one feature may be shown in one drawing, and the
best mode of another feature will be called out in another drawing.

[0025] All publications, patents and applications cited in this
specification are herein incorporated by reference as if each individual
publication, patent or application had been expressly stated to be
incorporated by reference.

[0026] FIG. 1 shows an exemplary embodiment of the overall system
architecture of the inventive rapid response helium leak detection system
10 as installed in a Class 1, Division 1, Group D Hazardous Location
Enclosure 12 having wheels 14 for mobility. The enclosure 12 is
preferably a sealed stainless steel box sized at approximately 15 cu ft;
suitable access doors (not shown) are provided for installation and
service repair of the interior sub-systems. All apertures are sealed,
including the vias for sniffer probe hose input 16, facility power line
18, facility compressed air inlet line 20, leak detector exhaust line 22
and boost pump 190 2 exhaust line 24. Also sealed are an ambient
atmospheric pressure reference device 26, an enclosure overpressure
protection vent line 28, the several lines to and from the vortex cabinet
cooler 30 and a controller 32, which is accessible from the outside and
which communicates with the leak detector 44. The control panel includes
an input interface, display and visual and audible alarm, preferably an
alarm at the probe handle 90, and/or on the cabinet. The controller 32
includes a display, preferably integrated, and visible through a sealed
window 94 in the side wall or top wall of the cabinet. In the embodiment
wherein the controller and display are internal to the cabinet, the
system may include an externally accessible control panel, such as button
switch unit 96, that is sealed into the top or side wall of the cabinet
as illustrated in FIG. 1. The control system may also include wireless
link to a facility LAN system so that at any time, data from in-progress
testing of tanks can be observed and archived in system memory.

[0027] Internal of the sealed cabinet are a number of sub-systems,
including an enclosure protection and rapid exchange purge system 34,
which regulates and monitors pressure of the sealed enclosure 12 and
rapidly removes and prevents flammable vapor accumulation within the
enclosure. The protection and rapid exchange purge system 34 comprises a
pressure differential-actuated line cut-off switch 36 in the incoming
power line 18. The switch 36 outs off power 38 to the pumps 40 and 42 and
to the helium leak detector unit 44 itself, in the event that the
pressure inside the cabinet 12 falls below a preset minimum, by way of
example, 0.15'' c.w. within the cabinet. This power-shut-off provides
protection against spark ignition of vapors that may enter the cabinet in
hazardous environments. The purge unit may also be visible through a
sealed window in the side wall of the cabinet (not shown).

[0028] In addition, the rapid exchange purge system regulates the pressure
in the enclosure 12 as follows: A sensed reference 26 to the pressure in
the ambient environment in which the mobile enclosure is located, e.g., a
fueling depot area, is compared to the internal pressure reference inside
the enclosure 46. The differential of these pressures determines the
state of the pressure control valve 48 that is in one branch 50 of
compressed air teed line 52 inlet from facility compressed air 20. When
the pressure differential is below 0.15'' c.w., as in the above example,
the Rapid (Air) Exchange Sequence is initiated, with valve 48 opening to
provide compressed air, for example, supplied at 80 psig, via outlet 54
into the interior of the enclosure, thus maintaining the overpressure in
the cabinet to prevent infiltration of ambient hazardous vapors. When the
internal pressure P exceeds a preset value, approximately 0.65'' c.w.,
the Enclosure Protection Vent 28 automatically opens and the air in the
enclosure begins to be exchanged out as compressed air is inlet via valve
48. Vent 28 is also a spark arrester type vent.

[0029] The compressed air is supplied taster than the vent 28 can release
enclosure air, so the internal enclosure pressure continues to rise. Once
the internal enclosure pressure reaches 2.5'' c.w., the timer of the
Rapid Exchange Sequence starts. The exchange period is typically set at
15 minutes, during which approximately 4 enclosure volumes are exchanged
out. Thus, during the RES the pressure within the enclosure can rise to
approximately 4.5'' c.w., during which the EPV is open, allowing for a
purging of the enclosure with the 4× volume change of fresh air.

[0030] After the RES time period ends, the compressed air inlet valve 48
closes, the EPV stays open until the pressure in the enclosure drops to
1.5'' c.w. This value for closure of the EPV is set by the operator via
the Enclosure Pressure Control valve. At that point the electrical power
to the system is restored by closure of switch 36. Normal operation
continues with the Purge system maintaining the pressure P2 within the
enclosure 1.2 at 1.5'' c.w. and the power ON. If the enclosure pressure
were to fall below 0.15'' c.w. the whole repressurization/purge cycle is
repeated.

[0031] In addition, the input compressed air provides a cooling function
by a purely mechanical system, comprising the compressed air 52 feeding a
second branch 56 into the vortex cooler 30. The cooled portion of the
compressed air is fed back into the cabinet via line 58. Of course,
cooler air inlet via line 58 contributes to the internal pressure, such
that the valve in the vent 28 may open relatively simultaneously,
providing rapid venting and continuous supply of clean dry cooled air
into the cabinet. The vortex cooler is actuated by a mechanical thermal
actuator 60 which opens a valve in line 56 permitting the compressed air
to flow through the vortex cooler 30. The warm exhaust stream from the
cooler is not shown, but it exhausts to ambient, that is outside of the
cabinet.

[0032] Pumps 1 and 2 are powered by line 38, and are in parallel with a
manifold 62 that splits the incoming gas sample from the sniffer probe
16. The pump #2 provides a booster draw which brings a large volume of
sample gas into the manifold within the enclosure which is exhausted out
the exhaust line 24. A portion of the gas sample is diverted to the leak
detector 44 at a rate at which it can handle, and that portion of sample
gas is drawn through the leak detector by pump #1 and then exhausted to
the exterior via exhaust 22. Since the sample gas is uniform, the ppm of
He in the main stream 64 is the same as in the detector stream 66. Thus,
the process of the invention comprises the step of sampling only a
portion of the entire sniffer input stream, which can be transported
faster to the detector by increasing fluid (gas) flow through the use of
a larger capacity booster pump.

[0033] FIG. 2 shows, in block diagram form, the operation of the inventive
rapid response helium leak detection system pressure and temperature
control system of FIG. 1, so FIG. 2 should be read together with FIG. 1.
The left side of the diagram shows the operation of the purge control
system while the right half of the diagram shows normal operation and
cooling when temperature goes over its set point. Referring the left half
of the diagram, the enclosure pressure set point range is entered in
controller 32, with the low set point at 0.15'' c.w., and the high set
point at 1.5'' c.w. as the selected operational range. Where the pressure
falls below 0.15'' c.w., at condition 68, as sensed by the differential
between ambient 26 and internal 46, the purge protection system 34 is
triggered to open power line switch 36 to the OFF mode, 92, cutting off
power 38 to the leak detector 44 and the vacuum pumps 40, 42. At the same
time the purge cycle is activated by opening valve 48 to provide
additional compressed air 54 into the enclosure to repressurize the
enclosure. When the purge cycle is finished and the enclosure internal
pressure is restored to 1.5'' c.w., Normal operation mode is resumed, and
the power is switched to the ON mode, 80, by the closing of switch 36.
When the compressed air valve 48 is opened, and the Cabinet pressure, P2,
exceeds approximately 0.65'' c.w., the vent 28 opens permitting purge air
exchange.

[0034] Where the 26, 46 pressure differential condition 70 is now above
the low set point of 0.15'' c.w. and below the high set point of 1.5''
c.w., the system is operating normally, the enclosure purge protection 34
closes switch 36 and power 38 is provided to the leak detector 44 and the
two vacuum pumps 40, 42 to draw gas sample through sniffing probe 16.
Where the temperature is sensed in the cabinet by temperature sensor T,
see FIG. 1, as above the set point 30° C., condition 74, the
vortex cooler 30 is activated by thermal actuator 60 to provide cooling
air 58 into the enclosure.

[0035] This system operation as set forth in FIGS. 1 and 2 is further
described by way of an implementation example in the three related FIGS.
3-5, in which FIG. 3 is a block diagram of the operation of the purge
cycle of the inventive enclosure purge system sub-assembly, FIG. 4 is a
block diagram of the operation of the vortex cooler sub-system of the
inventive enclosure and FIG. 5 is a block diagram of the operation of the
leak detector sub-system of the inventive enclosure. In this example of
operation, the following parameters are established:

[0036] P1 is the ambient atmospheric pressure;

[0037] P2 is the internal enclosure pressure;

[0038] Ps is the facility compressed air supply pressure in #/sq. in.
(PSIG);

[0041] Tset is the vortex cooler 30 set point of thermal actuator 60 in
°C.

In this example, as shown in FIG. 3, the following settings are entered
into the controller 32:

[0042] Ps=80-100 PSIG;

[0043] Tset=30+ C.;

[0044] Pset=0.65'' c.w.; and

[0045] Purge cycle time=15 minutes.

[0046] In normal operation, the rapid exchange purge unit 34 automatically
maintains the enclosure at the following conditions:

[0047] P2=1.5'' c.w.;

and the purge cycle is initiated if the pressure falls such that:

[0048] P2<0.15'' c.w.

When the pressure falls below the minimum the purge cycle is initiated
for a period of 15 minutes.

[0049] As shown in FIG. 3 upon initiation of the purge cycle 76, the timer
is started at t=0, the output pressure from the facility compressed air
supply into the enclosure is supplied by opening valve 48 at a delivery
pressure of Ps=80 psig and the detector 44 and pumps 40, 42 are shut off
by cut off of the electrical supply 38 by opening switch 36. The cycle
timer counts up at 78. If t>15 minutes, the YES branch is followed,
and if the pressure in the enclosure, P2=1.5'' c.w., the electrical
supply is activated ON, 80, by closure of switch 36. If t<15 minutes,
the NO branch is followed, the purge input of air via valve 48 and supply
20, 50 continues with the pressure in the enclosure P2 being monitored at
82 through the reference sensors 26, 46. Where the pressure in the
enclosure, P2>0.65'' c.w., the YES branch is followed, the exhaust
pressure valve (EPV) 28 automatically opens, and the fresh dry compressed
purge air continues to be supplied via valve 48, the net result being to
clear the enclosure through the remainder of the purge cycle. Where the
pressure in the enclosure remains <0.65'' c.w., the NO branch is
followed, the exhaust pressure valve 48 remains closed, and the
compressed air P, 54, continues to be supplied via 20, 50, 48 as the
cycle continues.

[0050]FIG. 4 shows the operation of the vortex cooler 30. The thermal
actuator 60 is set to activate at Tset>30° C. So long as the
temperature in the enclosure remains below Tset, the valve 84 (see FIG.
1) remains closed 84a as shown by the NO branch of FIG. 4. Where the
temperature exceeds Tset, the YES branch of the diagram is followed, the
valve 84 is opened, 84b, and cooled air 58 is supplied to the interior of
the enclosure 12. Note that both the purge operation of FIG. 3 and the
cooling of FIG. 4 can operate at the same time. That is, if the
temperature in the enclosure rises beyond Tset, the cooling commences. If
this results in overpressure P2>0.65'' c.w., the EPV 28 opens and the
hot air in the enclosure interior is flushed. If during that cooling
event, the purge cycle is initiated, there can be two sources of fresh
dry facility air provided, through both the vortex cooler 58 and through
the rapid exchange purge system 34, 54.

[0051]FIG. 5 shows schematically the operation of the helium leak
detection system 44. The leak detector operation is initiated at the
control panel 32 with the Pass/Fail detection level, Lset, being preset
at 86. The detector 44 is put into operation by powering the detector and
pumps 40 and 42 to draw sample from the probe 16. The sample stream is
split by the manifold 62, and the minor detection portion is inductively
drawn through the detector 44 by vacuum, pump #1, 40. The detector
reports the He values detected 88 to the controller 32. Where the Lset
value is not exceeded, the NO branch, the probe sniffing may continue.
Where the Lset is exceeded, the YES branch, an alarm signal 90 is sent to
the probe so the operator may mark the location of the leak on the tank
being sniffed.

[0052] In accord with the inventive principles described and shown herein,
an improved He leak detector takes in a sample of gases through a
approximately 60' of sniffing line, detects the trace amount of helium in
the sample by means of a helium sensitive sensor, and converts the sensor
signal to quantitative leak rates. To provide high speed transport of
sample from the induction sniffer probe, which is being passed over the
surface of a tank over-pressured with a test mixture of helium and air, a
second, booster vacuum pump is provided in parallel to the detector
vacuum pump (which is located downstream of the detector). This provides
a draw greater than can be handled by the detector, but results in rapid
transport of a sample stream to the detector enclosure, where a manifold
splits it into two streams, a small detector sample portion suitable in
volumetric rate tor the detector, and a major portion that is exhausted
exterior of the enclosure without passing through the detector.

[0053] The system also houses the detector and pumps within a sealed,
fresh air-purged enclosure that permits the use of the electrical
components of the detection system in Class 1, Division 1, Group D
Hazardous Environments. The rapid exchange purging system operates on a
supply of fresh, dry compressed air provided by the facility where the
tanks are being tested for leaks. The purging system regulates and
monitors pressure of the sealed enclosure relative to the ambient
environment, and prevents flammable vapor accumulation within the
enclosure. During a purge cycle, the system rapidly removes 4 or more air
exchanges and maintains a positive pressure in the enclosure to prevent
infiltration of vapors. The purge system includes an electrical power
controller that monitors the purging operation and controls enclosure
power to all internal electrical components.

[0054] The system also may include a vortex-type cooler to cool the air in
the enclosure when located in a hazardous environment, using only the
fresh compressed air supply to generate the cooling. The vortex cooling
system is entirely mechanical that requires no electrical components. The
cooling air produced by the vortex cooler and supplied to the interior of
the enclosure displaces hot air in the enclosure that is vented into the
hazardous area outside the enclosure via a spark arrester vent that is
mechanically biased normally closed, but will automatically open at a
preselected interior pressure.

[0055] In its broad aspects, the system of the invention for high speed
detection of He leaks from vessels pressurized with He tracer gases
comprises: Installed in a Class 1, Division 1, Group D hazardous purged
air enclosure that permits use of all electrical components associated
with leak detection components and the purge air system is a He tracer
gas probe unit having a negative pressure nozzle for sniffing He leaking
from He tracer gas-pressurized vessels to provide probe samples; a
conduit having a first end connected to an output of said probe unit for
conveying said probe samples from sniffed vessels; a pumping manifold
system having an inlet connected to a second, distal end of said conduit
to receive said probe samples; a detector unit including a He sensor
which produces a He detection signal and converts said signal into
quantitative leak rates; and said manifold system including a pair of
pumps oriented in parallel in which a first pump is disposed downstream
of said detector unit to draw a portion of said probe sample into contact
with said He sensor, and a second pump providing a negative pressure
rapid transfer boost of said probe sample from said probe unit nozzle to
said manifold to reduce the transit time from the probe to the He sensor
to permit near real time He leak detection.

[0056] In its broad aspects, the method of the invention for high speed
detection of He leaks from vessels pressurized with He tracer gas in a
hazardous environment comprises the steps of: pressurizing a vessel to be
tested for leaks with a He-containing tracer gas; sampling selected areas
of the exterior of said vessel to be tested with a negative pressure
probe to obtain a sample stream volume of gas that may contain He leaking
from said test vessel; transferring at high speed said entire volume of
said sample stream to a manifold by a first negative pressure device;
splitting-off at said manifold a minor portion of said entire sample
stream as a detection stream; drawing said detection stream through a He
sensor by a second negative pressure device, said He sensor providing a
signal upon detection of the presence of trace gas He in said detection
stream; and converting in near real time said detection signal into
quantitative leak rates of said test vessel, said manifold, sensor and
negative pressure devices being disposed in a sealed, purge air enclosure
that permits use of all electrical components associated therewith.

[0057] It should be clear from the principles of the invention set forth
herein, including the examples given, that it will be straightforward for
those skilled in the art to adjust the various parameters of the
inventive system, such as pressures, set points, time durations and the
like, to suit a particular detection application situation for various
tank or vessel sizes, types, and service use.

INDUSTRIAL APPLICABILITY

[0058] It is clear that the inventive rapid response helium leak detection
system of this application has wide applicability to the leak detection
industry, and more particularly to the rapid detection of leaks in all
types of vessels in hazardous environments, including aircraft fuel
tanks, and the like. Since the inventive enclosure is mobile and can
operate in Class 1, Division 1, Group D Hazardous Locations, it has the
clear potential of becoming adopted as the new standard for apparatus and
methods of He leak detection under such conditions.

[0059] It should be understood that various modifications within the scope
of this invention can be made by one of ordinary skill in the art without
departing from the spirit thereof and without undue experimentation. For
example, the enclosure configuration can have a wide range of designs to
provide the functionalities disclosed herein. Likewise the operation may
be controlled and configured to give a wide range of quantitative leak
rates before alarms are triggered, and may include archival recording
system to record all sensing of a given tank, aircraft or group of tanks.
This invention is therefore to be defined by the scope of the appended
claims as broadly as the prior art will permit, and in view of the
specification if need be, including a full range of current and imam
equivalents thereof.